Expansion bail anchor and method

ABSTRACT

An expansion anchor assembly for a mine roof bolt having a tapered plug, expansion leaves, a bail and a removable holding ring configured to hold the expansion anchor assembly in an assembled position is disclosed. The tapered plug is configured to be threaded onto the mine roof bolt and defines plug channels to encourage symmetrical resin flow past the tapered plug. The bail defines a medial opening through which the mine roof bolt extends.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to expansion bail-type mine anchors and methods of their use.

2. Description of the Prior Art

In underground mining operations generally, unsupported rock formations may be reinforced by bolts inserted into bore holes that have been drilled into the rock formations. These bolts may then be secured within the bore hole to the rock formations by utilizing an expansion anchor positioned on the distal end of the bolt. The free end of the bolt extending into the mine passageway receives a bearing plate. Rotation of the bolt within the bore hole expands the expansion anchor to engage the rock surrounding the bore hole. The expansion of the expansion anchor brings the bolt under tension and further compresses the rock strata between the bearing plate and expansion anchor to form a beam of rock strata that resists forces that could stress the rock formations. Accordingly, expansion anchors are widely used for supporting and reinforcing rock formations in underground mining operations.

One type of expansion anchor includes a bail-type anchor having a bail connecting two leaves of a hollow shell surrounding a tapered wedge or plug. The tapered plug is generally internally threaded and is threaded onto the distal end of a bolt. Upon application of a rotation of the bolt, the plug threads downwardly on the bolt, thereby forcing the shell to expand into gripping contact with the bore hole wall.

Other expansion anchors include an expansion shell anchor having three or four upwardly extending expansion leaves of a hollow shell commonly joined at one end opposite a tapered plug that is threaded onto a bolt. Upon rotation of the bolt, the leaves of the shell expand into gripping contact with the bore hole formed in the rock formation through the axial movement of the tapered plug engaging the shell.

Typically, there are several methods employed for securing a mine roof bolt within a bore hole. The bolt may be dry anchored in the rock formation by engagement of an expansion anchor, either the bail-type or the expansion-shell type, positioned on the end of the bolt within the rock formation. Other methods include chemically anchoring the bolt by bonding the bolt with resin to the rock formation surrounding the bore hole, or using both an expansion anchor and resin together to retain the bolt within the bore hole. Resin is generally provided in a two-compartment cartridge, one compartment for each of a curable resin composition and a catalyst or curing agent. The resin cartridge is inserted into the blind end of the bore hole in advance of the mine roof bolt. Upon insertion of the mine roof bolt and rotation thereof, the cartridge is shredded and its contents are mixed. Proper mixing of the curable resin composition and curing agent without interference from the cartridge housing are important to achieve good chemical anchoring.

Bail-type anchors are traditionally difficult to use with chemical anchoring. As the resin mixes and cures, the bail of traditional bail-type expansion anchors has a tendency to bias and become cocked, compromising the ability of the anchor assembly to properly expand and engage the rock formation.

SUMMARY OF THE INVENTION

The present invention includes an expansion shell assembly for a mine roof bolt comprising: (i) an expansion shell comprising a pair of leaves, the leaves each having an outer surface for engaging a wall of a mine roof bore hole and an inner surface; (ii) an internally threaded plug received between the inner surfaces of the leaves for threading onto a mine roof bolt, an outer surface of the plug defining a resin groove; and (iii) a bail comprising a pair of legs and a medial member therebetween, each leg being attached to one leaf, the medial member defining an aperture through which a mine roof bolt extends. The present invention also includes a mine roof bolt comprising an elongated member having a threaded portion and the afore-described expansion shell assembly threaded thereon.

The present invention further includes a method of supporting a mine roof comprising: (i) inserting a mine roof bolt into a bore hole containing a frangible curable resin cartridge, the mine roof bolt comprising an elongated member having a threaded portion and an expansion shell assembly received on the threaded portion of the expansion shell comprising: (a) an expansion shell comprising a pair of leaves, the leaves having an outer surface and an inner surface; (b) an internally threaded plug received between the leaves inner surface and threaded on the threaded portion, an outer surface of the plug defining a resin groove; and (c) a bail comprising a pair of legs extending from a medial member defining an aperture, each leg attached to one of the leaves, wherein the elongated member extends through the aperture; (ii) rupturing the resin cartridge; and (iii) rotating the mine roof bolt such that resin is mixed and flows through the resin groove and the expansion shell expands and engages the bore hole wall.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded side view of an expansion bail anchor assembly in accordance with the present invention;

FIG. 2 is a side view of the expansion bail anchor assembly of FIG. 1 showing the expansion bail anchor installed on a threaded end of a bolt and positioned in a bore hole in an unengaged state;

FIG. 3 is a side view of the bolt with expansion assembly of FIG. 2 showing the expansion assembly during installation;

FIG. 4 is a perspective view of the bolt with expansion assembly of FIG. 3 after installation;

FIG. 5 is a side view of the partially assembled expansion assembly shown in FIG. 1;

FIG. 6 is a side view of the expansion assembly of FIG. 5, with a retaining ring;

FIG. 7 is a side view of the expansion assembly of FIG. 1 installed on a threaded sleeve positioned at a proximal end of a cable bolt;

FIG. 8 is a side view of the expansion assembly of FIG. 1 installed on a threaded sleeve positioned at a distal end of a cable bolt;

FIG. 9 is a side view of the expansion assembly of FIG. 1 installed on a threaded sleeve positioned between the distal and proximal ends of a cable bolt;

FIG. 10 is a perspective view of another embodiment of the expansion assembly of the present invention;

FIG. 11 is a plan view of the bail used in the expansion assembly of FIG. 5;

FIG. 12 is a plan view of the bail used in the expansion assembly of FIG. 10; and

FIG. 13 is a plan view of another embodiment of a bail.

DETAILED DESCRIPTION OF THE INVENTION

For purposes of the disclosure, the terms “upper”, “lower”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom” and derivatives thereof shall relate to the invention as it is oriented in the drawing figures generally. However, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and methods illustrated in the attached drawings and described in the written description are simply exemplary embodiments of the invention. Hence, specific dimensions and other physical and spatial characteristics related to the embodiments disclosed herein are not to be considered as unduly limiting the present invention.

Referring to the drawings, and particularly to FIGS. 1-4, there is shown a mine roof bolt 10 bearing a bail-type expansion assembly 12. The mine roof bolt 10 is shown inserted into a bore hole 14 surrounded by rock strata 16 in FIGS. 2-4 and including a rod 18 having a drive end 20 that includes drive head 22 fixed to the rod 18. A bearing plate 24 is generally positioned between drive head 22 and the mine roof surface 26. Threaded distal end 28 of rod 18 receives the expansion assembly 12. The expansion assembly 12 generally includes a bail 30, a tapered plug 32, a plurality of expansion leaves 34 connected by the bail 30 and may further include a removable retaining ring 36. The bail 30 is shown in more detail in a flattened state in FIG. 11 and includes a medial portion 38 and a pair of legs 40 that may be integrally formed therewith. An opening 42 is defined in medial portion 38 for receiving bolt threaded end 28 therethrough. Legs 40 are fixed to leaves 34 in a conventional manner, such as via an attachment member 44, such as a pin extending through both as shown in FIGS. 5 and 6. Attachment member 44 prevents bail 30 from moving in directions parallel to the medial axis. Alternatively, attachment member 44 may be formed integrally with the expansion leaf 34 or bail legs 40.

As shown in FIG. 5, the tapered plug 32 defines a threaded internal bore 46 for threading onto and traveling along a threaded end 28 of mine roof bolt 10. Plug 32 includes an upper plug surface 48 that may be planar or frustoconical as shown. A pair of channels 50 for receiving bail legs 40 are defined in opposing sides of plug 32 and upper plug surface 48.

A pair of legs 52 extend from main portion 54 of plug 32, thereby forming tapered surfaces 55. Main portion 54 further defines a plurality of longitudinal plug grooves 56. The longitudinal plug grooves 56 may be provided to encourage passage of resin as described below.

Expansion leaves 34 may have a serrated outer surface 58 that generally extends circumferentially about the longitudinal axis and tapering edge surfaces 60 along the serrated outer surfaces 58. In an assembled position, as shown in FIGS. 5 and 6, the leaf tapering edge surfaces 60 taper toward each other and abut corresponding plug tapered surfaces 55. The distal end of leaves 34 may define rows of channels 62 formed therein.

When assembled (FIG. 6), bail medial portion 38 seats on upper plug surface 48. In one embodiment, bail medial portion 38 is generally ring-shaped with opposing sides of the ring having a reduced dimensional portion 66 as shown in FIGS. 5 and 11. Other configurations for a bail medial portion may be used. As shown in FIG. 12, bail 130 includes bail medial portion 138 that is generally ring-shaped. Alternatively, as shown in FIG. 13, a bail 230 having a bail medial portion 238 with reduced dimensional portions or notches 266 may be used. Notches 266 are sized and positioned to align with plug grooves 56 as shown in FIG. 10. Reduced dimensional portion 66, 266 is sized and configured to prevent interference of bail medial portion 38 (and/or 238) from interfering with use of plug grooves 56.

Additionally, the reduced dimension portion 66, 266 may encourage the even flow of resin on either side of expansion anchor 12 and help prevent cocking of the expansion anchor assembly 12. Accordingly, the reduced dimension portion 66, 266 may be formed symmetrically in any given embodiment. Further, the reduced dimensional portion 66, 266 may encourage resin to flow through the plug grooves 56 to further encourage the proper alignment of the expansion anchor assembly 12 into the bore hole 14. In addition, reduced dimensional portion 66, 266 may further encourage shredding and mixing of a resin capsule and/or resin.

In use, a two-component (catalyst and curable resin) capsule 80 is inserted into the blind end of a bore hole 14. The mine roof bolt 10 bearing expansion anchor assembly 12 is inserted into bore hole 14 with bearing plate 24 positioned thereon.

Retaining ring 36, which may be formed of a breakable and/or flexible thermoplastic material, is positioned around the expansion leaves 34 and holds the expansion anchor assembly 12 together, while the bolt 10 is being inserted into the bore hole 14. As the bolt 10 is inserted into bore hole 14, the retaining ring 36 remains outside the bore hole 14 (FIG. 2) and is removed. Bolt 10 contacts and ruptures the capsule 80. Rotation of the bolt 10 about its longitudinal axis mixes the curable component and catalyst component, generating resin 82. Rotation of the bolt 10 also causes plug 32 to travel toward the mine roof surface 26 on the threaded portion end 28, thereby forcing expansion leaves 34 to spread apart and engage the rock strata 16. The resin 82 flows downwardly around and past the reduced dimensional portion 66, 266 and into plug grooves 56 and the leaf channels 62, each facilitating the flow of resin 82 over the expansion anchor assembly 12.

It should be appreciated that the improved expansion anchor assembly 12 of the present invention may be implemented in chemical anchoring or mechanical anchoring applications, although the invention has been illustrated showing resin bonding to provide chemical anchorage of the expansion anchor assembly 12.

As can be seen in FIGS. 7-9, a cable bolt as described in U.S. Pat. No. 6,270,290, incorporated herein by reference, may include the expansion anchor assembly 12 of the present invention. Cable bolt 310 includes a multistrand cable 311 adapted to be received within a bore hole. The cable 311 is preferably formed of steel strands conforming to appropriate ASTM standards for a given application. The cable 311 may generally have multiple strands with a medial strand helically enclosed by outer strands. Cap 312 may be included to provide integrity to the end of the cable bolt 310.

The cable bolt 310 may include “birdcages” 313 positioned where the strands of the cable 311 are separated and partially unwound from each other. A nut or washer 318 may optionally be positioned on the medial strand of the cable 311 in the birdcage 313 to assist in maintaining spacing between the medial strand and the surrounding strands. The provision of spaced birdcages may also enhance the mixing and/or shredding of resin capsule 80 during installation, as well as increase the bond strength of the resulting chemical anchorage.

Cable bolt 310 includes a conventional drive head 322 (for rotating the bolt 310) and barrel and wedge assembly 324 (for tensioning the bolt). A sleeve or shaft 326 having a central bore for receiving the cable 311 is fixed to the cable 311, such as by crimping or swaging. The shaft 326 defines exterior threads 328 onto which expansion assembly 12 is threaded.

In use, cable bolt 310 is inserted into a bore hole following insertion of a resin cartridge as with bolt 10 and ruptures the cartridge. The cable bolt 310 is rotated using drive head 322 to mix the contents of the resin cartridge and cause expansion assembly 12 to grip the bore hole wall as described above in reference to bolt 10.

When used with a cable bolt, expansion assembly 12 may be positioned proximal to the drive end (as in FIG. 7), or may be positioned at the end of the cable 311 (per bolt 310A of FIG. 8) or intermediate the length of the cable 311 (per bolt 310B of FIG. 9). Bolts 310A and 310B include the shaft 326 at a desired location for mechanical anchoring. Stiffener sleeve 330 may be included to assist insertion of bolts 310A and 310B into a bore hole.

The invention has been described with reference to the preferred embodiments. Obvious modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. 

1. An expansion shell assembly for a mine roof bolt, comprising: an expansion shell comprising a pair of leaves, said leaves each having an outer surface for engaging a wall of a mine roof bore hole and an inner surface; an internally threaded plug received between said inner surfaces of said leaves for threading onto a mine roof bolt, an outer surface of said plug defining a resin groove; and a bail comprising a pair of legs and a medial member therebetween, each said leg being attached to one said leaf, said medial member defining an aperture through which a mine roof bolt is extendable.
 2. The expansion shell assembly of claim 1, wherein said medial member defines a recess aligned with said resin groove of said plug.
 3. The expansion shell assembly of claim 2, wherein said medial member is ring-shaped and two opposing portions of said medial member have a reduced radial dimension.
 4. The expansion shell assembly of claim 2, wherein said recess comprises a notch in said medial portion.
 5. The expansion shell assembly of claim 1, wherein an upper surface of said plug receives said bail medial portion and said plug defines a pair of bail grooves receiving a leg of said bail.
 6. The expansion assembly of claim 5, wherein said plug has a sloped upper surface.
 7. A mine roof bolt comprising: an elongated rod, said rod having a drive end and a threaded portion; and an expansion shell assembly as claimed in claim 1 threaded onto said rod threaded portion.
 8. A mine roof bolt comprising: an elongated cable, said cable having a drive end and a distal end; a threaded member fixed to said cable; and an expansion shell assembly as claimed in claim 1 threaded onto said threaded member.
 9. The mine roof bolt of claim 8, wherein said threaded member is fixed to said cable at said cable distal end.
 10. The mine roof bolt of claim 8, wherein said threaded member is fixed to said cable at a position intermediate said cable drive end and said cable distal end.
 11. In an expansion shell assembly for a mine roof bolt comprising: (i) an expansion shell comprising a pair of leaves, each said leaf having an outer surface for engaging a wall of a mine roof bore hole and an inner surface; (ii) an internally threaded plug received between said leaves for threading onto a mine roof bolt; and (iii) a bail comprising a medial member and a pair of legs extending from opposing sides thereof, the improvement comprising: said bail medial member defining a recess and said plug defining a resin groove extending from an upper surface of said plug and being aligned with said bail recess, such that resin is flowable through said bail recess and into said plug groove.
 12. The expansion shell assembly of claim 11, wherein said medial member is ring-shaped and two opposing portions of said medial member have a reduced radial dimension.
 13. The expansion shell assembly of claim 11, wherein said plug defines a plurality of resin grooves, said resin grooves being aligned with said recess.
 14. The expansion shell assembly of claim 11, wherein said bail recess comprises a notch defined in said medial member.
 15. A method of supporting a mine roof comprising: (a) inserting a mine roof bolt into a bore hole containing a frangible curable resin cartridge, the mine roof bolt comprising an elongated member having a threaded portion and an expansion shell assembly received on the threaded portion, the expansion shell assembly comprising: (i) an expansion shell comprising a pair of leaves, the leaves having an outer surface and an inner surface; (ii) an internally threaded plug received between the leaves inner surface and threaded on the threaded portion, an outer surface of the plug defining a resin groove; and (iii) a bail comprising a pair of legs extending from a medial member defining an aperture, each leg attached to one of the leaves, wherein the elongated member extends through the aperture; (b) rupturing the resin cartridge; and (c) rotating the mine roof bolt such that resin is mixed and flows through the resin groove, and the expansion shell expands and engages the bore hole wall.
 16. The method of claim 15, wherein the elongated member comprises a rod.
 17. The method of claim 15, wherein the elongated member comprises a multi-strand cable.
 18. The method of claim 17, wherein the threaded portion comprises a tube fixed to the cable.
 19. The method of claim 18, wherein the tube is fixed to the cable at a position between the drivehead and the end of the cable.
 20. The method of claim 15, wherein the bail medial member defines a recess aligned with the plug resin groove so that resin flows through the recess and resin groove. 